The invention relates generally to power-driven conveyors and more particularly to conveyors having rollers for manipulating the trajectory of articles through a conveyor system.
Many package- and material-handling applications require that conveyed articles be diverted to a side of a conveyor. Two examples are sorting articles off the side of a belt and registering articles against the side of the belt. U.S. Pat. No. 6,494,312, “Modular Roller-Top Conveyor Belt with Obliquely-Arranged Rollers,” Dec. 17, 2002, to Costanzo discloses a conveyor system in which cylindrical rollers mounted in a conveyor belt on axles oblique to the direction of belt travel are actuated by underlying bearing surfaces on which the oblique rollers ride as the belt advances in the direction of belt travel. The contact between the rollers and the bearing surfaces causes the rollers to rotate as the belt advances. The rotation of the oblique rollers pushes articles atop the rollers across the conveyor belt toward a side of the conveyor. These oblique-roller belts work extremely well on planar bearing surfaces as long as the rollers are arranged to rotate at an angle between the direction of belt travel (defined as a roller angle of 0°) and about 30° or so from the direction of belt travel. For roller angles greater than 30°, the rollers slip too much on the planar bearing surfaces.
U.S. Pat. No. 6,968,941, “Apparatus and Methods for Conveying Objects,” Nov. 29, 2005, to Fourney describes an improved bearing surface that accommodates a much greater range of roller angles. Instead of using a planar bearing surface, Fourney uses the outer peripheries of actuating rollers arranged to rotate on axes in the direction of belt travel. As the conveyor belt advances, the oblique belt rollers roll on the underlying actuating rollers, which are also caused to roll on their axes. Because the bearing surface on the periphery is rolling, slip is reduced and greater roller angles can be accommodated. The greater roller angles permit much sharper article-diversion trajectories than are possible with a planar bearing surface. But actuating rollers are more expensive and slightly more complicated than simple planar bearing surfaces.
U.S. Pat. No. 7,588,137, “Conveyor Belt Having Rollers that Displace Objects,” Sep. 15, 2009, to Fourney describes a conveyor belt that includes multiple roller sets used to divert objects from the conveyor belt. The angles along which articles can be diverted from the conveyor are limited.
U.S. Patent Publication 2013/0192954, published Aug. 1, 2013 and entitled “Multi-Directional Roller Assembly” (now U.S. Pat. No. 8,978,879), the contents of which are herein incorporated by reference, describes a multi-directional roller assembly that may be driven by a conveyor belt below the assembly. The same conveyor belt conveys articles to and from a roller plate housing an array of multi-directional roller assemblies. The roller assemblies manipulate the trajectory of the articles, or pass the articles straight along the roller plate and back onto the conveyor belt. The conveyor belt is diverted below the roller plate to drive the roller assemblies. The conveyor belt may experience high tensions. Furthermore, the transition of articles off the conveyor belt, onto the roller plate and back onto the conveyor belt may alter the desired spacing between articles, in addition to presenting unnecessary instability.